1. Field of the Invention
The present invention relates to a method of writing servo tracks for a disk file apparatus or, in particular, to a method of writing servo tracks for a disk file apparatus such as a magnetic disk unit used as an external recording apparatus for computers, in which the quality of the servo tracks formed on the disk medium can be improved.
2. Description of the Related Art
In recent years, disk file apparatuses such as a magnetic disk unit and an optical disk unit have been used as an external storage unit for computers. In such a disk file apparatus, the storage capacity of the disk medium is increasing year by year. In the case where the size of the disk medium is fixed, therefore, the increased storage capacity makes it necessary to increase the TPI (tracks per inch) by narrowing the pitch of the recording tracks on the disk medium.
In a disk file apparatus such as a magnetic disk unit, on the other hand, the recording tracks formed on the disk medium are concentric about the rotational center of the disk. Each recording track is formed by each head of the disk unit by writing a servo pattern over the entire surface concentrically after the disk medium is assembled in the disk unit at the time of manufacture of the disk unit. Each recording track includes a servo zone having written therein servo information in advance and a data zone for recording data. The servo information is used for detecting a deviation between the center of the head and the center line of the recording track, and is written offset to the recording track. The operation for writing the servo pattern including the servo information is called servo track writing and, in the description that follows, the operation for writing the servo pattern will sometimes be referred to as the SYW.
In the STW for the conventional disk drive, first, a reference signal providing a time reference for writing a servo track is written in a portion other than the recording track on the disk medium by a fixed head (normally called a clock head, a reference head, etc.) loaded from outside the disk drive (which is also called DE, for disk enclosure). This reference signal contains a burst signal of a predetermined frequency and an index signal indicating a reference position. The servo tracks on the disk medium are written with the head in the DE in synchronism with the reference signal.
When performing the STW operation using the head in the DE, the head is moved on the disk medium by being pushed with a push pin of a drive unit (servo track writer) external to the DE. In the case where the moving accuracy of the push pin is low, therefore, the problem of a deteriorated write quality (STW quality) of the servo track arises. Another probable cause of deterioration of the STW quality is the continuous vibration, asynchronous with the rotational frequency of the spindle motor, due to the bearing of the spindle motor for rotating the disk medium. Therefore, an improvement in the STW quality, in view of the asynchronous continuous vibration, is desired.